During the past few years, the transmission capacity of fiber optic networks has increased tremendously. As with much of technology, however, more is better, and the limitations of today's technology are impeding the ability of fiber optic networks to fulfill bandwidth demands.
Polarization dependent loss (PDL) is one of the limiting factors in high-capacity wavelength-division-multiplexing (WDM) systems. Many optical network components and erbium-doped fiber amplifiers (EDFA) have non-negligible PDL.
PDL leads to a number of problems in optical networks, such as fluctuation in the optical power and signal to noise ratio (SNR) and enhanced degradation of systems due to the interaction with polarization-mode dispersion (PMD).
Current efforts to control or compensate for PDL are based on the principal that the incidence angle of a crystal or glass is polarization-dependent. Therefore, by tuning the input angle or the position of the crystal or glass, the induced PDL value changes. Here, the induced PDL value is the difference between the maximum and minimum insertion loss for all possible input states of polarization (SOPs). However, such efforts are unable to provide limited variation in the PDL of a system.
Therefore, it is desirable to provide a variable PDL device that may be used to control and/or compensate for PDL in an optical system.